Jens Melinder. With financial support from CNES/CNRS convention #

Transcription

1 Jens Melinder With financial support from CNES/CNRS convention #

2 u u u u

3 The Lyman-α line in emission u The hydrogen Lyman-α emission line is the intrinsically brightest spectral feature from star-forming galaxies u Early attempts to detect the line in emission were largely unsuccessful. u The resonant nature of Lyα makes radiative transfer effects extremely important. u The escape fraction is often lower than what would be expected from observed nebular extinction. Lyα luminosities do not correlate well with global SFR Meier & Terlevich, 1981

4 Earlier imaging studies of Lyman-α in nearby galaxies Six starburst galaxies observed with HST/ACS (Östlin et al. 2009) u Showed that Lyα scattered out into a halo for the galaxies with net emission.two absorbers, four emitters. u Lack of extinction maps made it hard to account for nebular continuum in the continuum subtraction, and difficult to study the effect of dust on Lyα emission.

5 The original LARS The first 14 galaxies observed within the project showed that Lyα was found in emission in almost all cases (12/14) for a high SFR sample. Again, the imaging showed that Lyα scattered far out from where the photons were produced. u Imaging presented in Hayes et al. (2013, 2014), Östlin et al. (2014), Guaita et al u COS spectroscopy, Duval et al. (2016), Rivera Thorsen et al. (2015), u VLA HI observations, Pardy et al. (2015) u IFU spectroscopy, Herenz et al. (2016)

6 Jens Melinder Veronica Menacho (Stockholm) Matteo Messa (Stockholm) Johannes Puschnig (Stockholm)

7 The primary goals are to return detailed observations of the H I Lyα emission line, and to do so in a sample that is simultaneously as free from bias as possible, statistically meaningful enough to observe trends within the sample, and comparable in selection to galaxies observed in the high-z universe. Hayes et al. (2013) u 14 galaxies in the original LARS with EW(Hα)>100 Å + 28 galaxies with lower ssfr in elars at 0.027<z<0.14. Resolution ~ pc. u 5 blue compact dwarfs observed earlier (e.g. Haro 11, ESO 338-IG04) at 0.09<z< Tol u 5 ULIRGs at z~0.15

8 With ELARS the sample selection was relaxed to include galaxies with EW(Hα)>40 Å, and galaxies fainter in the UV. This selection targets galaxies that are expected to have lower EW(Lα). LARS

9 u Observing nearby galaxies in Lyαallow us to study the faintest emitters. u But are the nearby emitters similar to high redshift LAEs? u The original LARS galaxies are Lyman Break analogues, but ELARS contain more normal spiral galaxies. log Ly Luminosity [ erg s 1 ] C11 W14 G11 H10 C12 B11 R08 H15 LARS elars Redshift References: C11: Cowie et al. 2011, G11: Guaita et al. 2011, C12: Cantalupo et al. 2012, R08: Rauch et al. 2008, W14: Wold et al. 2014, H10: Hayes et al. 2010, B11: Blanc et al. 2011, H15: Henry et al. 2015

10 Observations HST Imaging u 3 FUV broadband filters (ACS/SBC) u 3 optical broadband filters (ACS/WFC3) u 2 NB filters for Hβand Hα(ACS/ WFC3) Other observations u Spectroscopy with COS (see talk by M. Hayes). u VLA/GBT H I of LARS+eLARS (see talk by M. Hayes) u Ground-based optical/nir imaging (NOT/CFHT) u IFU spectroscopy with PMAS and MUSE (see talk by C. Herenz)

11 LARS data reduction and line subtraction Reduced data AstroDrizzle, Cosmic rays Registration Generate PSF models PSF matching SDSS: NII, Z LaXs Lyα, Hα and Hβ line maps. SED fitted age and E(B-V) s maps

12 Continuum subtraction using LaXs Pixel SED fitting using 2 FUV filters and 3 optical broadband filters. Standard Χ 2 fitting on each pixel. u Starburst99 template spectra. u 3-4 free parameters, age of stellar population, stellar extinction, and stellar mass. u Two stellar populations, young+old. u Use extinction corrected Hαto estimate the nebular continuum. u Assumptions: Calzetti attenuation, Z and NII from SDSS, SSP SF history.

13 Lyα FUV Cont. Hα

14 Lyα FUV Cont. Hα

15 Lyα FUV Cont. Hα

16 LARS05 Typical Lyman α emitting galaxy in the original LARS. Quite compact dwarf irregular galaxy with some dust. Lyα seems to escape transverse to the major axis. EW(Hα) 314 Å EW(Lα) 30 Å f esc (Lα) 0.22 M L(FUV) 8e9 M 3.6e40 erg/s/å E(B-V) n 0.11

17 LARS05 Typical Lyman α emitting galaxy in the original LARS. Quite compact dwarf irregular galaxy with some dust. Lyα seems to escape transverse to the major axis. EW(Hα) 314 Å EW(Lα) 30 Å f esc (Lα) 0.22 M L(FUV) 8e9 M 3.6e40 erg/s/å E(B-V) n 0.11

18 ELARS01/NGC 6090 Galaxy merger and LIRG.Contains significant amounts of dust, but Lyα manages to escape even in the center of the system, maybe because of a patchy ISM structure. EW(Hα) 120 Å EW(Lα) 15 Å f esc (Lα) M L(FUV) E(B-V) n e10 M 4.0e40 erg/s/å

19 ELARS01/NGC 6090 Galaxy merger and LIRG.Contains significant amounts of dust, but Lyα manages to escape even in the center of the system, maybe because of a patchy ISM structure. EW(Hα) 120 Å EW(Lα) 15 Å f esc (Lα) M L(FUV) E(B-V) n e10 M 4.0e40 erg/s/å

20 ELARS10 Spiral galaxy at quite low inclination with significant dust. This system is a net absorber, but some Lyα radiation is able to escape from starforming regions in the arms. EW(Hα) 48 Å EW(Lα) -11 Å f esc (Lα) 0.0 M L(FUV) 3e10 M 1.4e40 erg/s/å E(B-V) n 0.27

21 ELARS10 Spiral galaxy at quite low inclination with significant dust. This system is a net absorber, but some Lyα radiation is able to escape from starforming regions in the arms. EW(Hα) 48 Å EW(Lα) -11 Å f esc (Lα) 0.0 M L(FUV) 3e10 M 1.4e40 erg/s/å E(B-V) n 0.27

22 Global measurements on LARS galaxies u Comparing two different apertures, both based on isophotal analysis of the line and continuum maps. - One aperture with an equivalent radius of 2 times the petrosian radius (estimated from the continuum UV map) - The other based on the faintest detectable isophotes in Lyα and continuum UV. u Errors from Monte Carlo simulations of the continuum subtraction. This is work in progress.

23 Lyα spatial distribution <2 r p20 > = 5 kpc <r totmask > =13 kpc Escape fractions may be severely underestimated when using smaller apertures. The fraction of net Lyα emitters in LARS/ELARS is: 35(12)/42 for a mask designed to include all Lyα (with EW(Lyα)>20) 29(11)/42 for a 2 r p20 radius aperture (with EW(Lyα)>20)

24 Lyα spatial distribution Do more extended Lyα emitters have higher escape fraction? -> No proper correlation found.

25 Lyα equivalent width distributions u The Lyα emitters with high escape fractions have the highest equivalent widths. u Galaxies with high EW(Lyα) all have low E(B-V) neb

26 Lyα equivalent width distributions u Low EW(Hα) (low ssfr) galaxies all have lower EW(Lyα) u High mass galaxies have low EW(Lyα)

27 How dust affects the escape fraction. Dust geometry Radiative transfer

28 Summary u Figuring out how and how and when Lyα radiation can escape is important for high redshift studies and can also give useful information about the ISM in star forming galaxies. u LARS is a sample of ~50 star-forming galaxies at z<0.15 with multi-wavelength observations available. The back-bone is the FUV-optical HST observations. u Lyα escape is mediated not by a single parameter, but by many different factors. Dust and neutral gas and how these components are distributed, as well as gas kinematics are important. All calibrated/stacked HST data and line maps for the 42 LARS galaxies will be released to the community in 2017.